Wheelchairs are well known forms of transportation that increase the mobility of the physically impaired. Wheelchairs are typically relatively small, single-person conveyances that generally comprise a seat base supported by a base frame which, in turn, is supported by two oppositely disposed rear drive wheels and front casters. The drive wheels are usually located behind the center of gravity of the wheelchair occupant and the front casters are swivel-mounted to the wheelchair frame to permit the occupant to maneuver the wheelchair with greater ease. The wheelchair is maneuvered by differentially driving the drive wheels.
Wheelchair occupants who have substantially no control over their lower extremities are prone to pressure sores as a result of having to remain in a fixed position for prolonged periods of time. Pressure sores are especially prominent in the pelvis region of the wheelchair occupant because the bones in the pelvis area are relatively sharp and prolonged pressure against the wheelchair occupant's skin may cause trauma to the skin tissue. Hence, it is important to reduce the number of pressure points against the wheelchair occupant's body. For at least this reason, pressure relieving wheelchair seats have been devised.
Wheelchairs generally comprise a seat sling supported by the seat base. The seat sling supports a seat cushion formed from a foam material and covered with a fabric covering. However, even foam material, such as foam rubber, has limited pressure-relieving characteristics. Hence, more recent innovations in technology have led to the development of gel cushions. Gel cushions are often used in conjunction with a foam seat cushion. Gel cushions typically comprise a membrane containing a relatively high viscosity gel. The advantage of gel cushions is that gel moves when pressure is applied to reduce the number of pressure points.
In addition to constant pressure points, sudden or abrupt shock or jolts to the wheelchair occupant may also cause tissue trauma. Minor abrupt changes in the pelvis area due to sudden jarring may cause injury to the wheelchair occupant's tissue. Beyond injury to the tissue, shock encountered by a wheelchair traversing rough terrain may also be transmitted through the wheelchair to the wheelchair occupant's spine, subjecting the upper torso of the wheelchair occupant to injury. Gel cushions have a limited effect on absorbing shock.
To reduce the risk of injury resultant from shock, wheelchairs have been equipped with shock absorbers. Shock absorbers are typically provided to absorb shock between the drive wheels and the base frame. The shock absorbers are typically of the mechanical type, embodying mechanically moving parts that require a dampening mechanism. The dampening mechanism is commonly of the hydraulic type, which requires an oil reservoir. Mechanical shocks are relatively heavy. Moreover, mechanical shocks can be costly, and this cost is often passed onto the wheelchair occupant, who is generally economically disadvantaged. A need exists for a lightweight, low-cost shock absorbing mechanism that employs few moving parts and that dampens shocks without the need for an oil reservoir to provide a relatively soft or smooth ride for the wheelchair occupant without bottoming out.
Often, even under the most ideal conditions, the softest cushions and most effective shock absorbers alone may not be affective in an assault against pressure sores. A completely static condition often results in muscle atrophy, which further contributes to tissue trauma or skin breakdown. To further reduce the risk of tissue trauma, it is desirable to frequently shift or change the position of the wheelchair occupant in the wheelchair. It is also desirable to change the position of the wheelchair occupant in accordance with the user's profile, or physical characteristics, or in accordance with various activities. Even able-bodied people normally shift and adjust their position according to various activities. A wheelchair occupant, however, is disadvantaged in that he or she is most frequently unable to orient his or her body in accordance with activities. A desired orientation of the wheelchair occupant is generally achieved by making appropriate adjustments to the wheelchair. Providing an element that offers resistance to shock and that permits variation in the wheelchair occupant's position may prove to be a cost effective alternative, or supplement, to the more conventional shock absorbers and adjustment elements.
In order to meet the needs of the physically impaired, wheelchairs must be versatile. Wheelchairs must be easily and readily adapted to accommodate the particular size and shape of the occupant. Wheelchairs must also be versatile in adapting to both ambulatory and recreational travel. Moreover, wheelchairs must be sufficiently durable to provide comfortable transportation over obstacles or irregular surfaces. A need exists for a shock-absorbing element that meets all these needs as well as the other needs set forth above.